1. Field of the Invention
The present invention relates to a hydraulic bearing motor, and particularly to a hydraulic bearing motor which, even though it is formed thin, can still satisfy features of exhibiting small NRRO, and vibration and shock resistance.
2. Description of the Related Art
In general, a bearing of a mass produced motor has a structure of supporting a motor shaft by using ball bearings. In such a bearing, however, steel balls as ball bearings, being in a state of rotating on a shaft or a support in principle, tend to generate noise. In particular, in an information home appliance mounted with an HDD (hard disk drive) recently becoming denser, a motor for driving the HDD at a higher speed generates larger noise from the bearing to cause a noise problem. Moreover, a bearing using the ball bearing tends to cause a large NRRO (non-resonant rotary oscillation) This causes read/write error in an HDD becoming denser.
Therefore, in recent years, development work is increasing about a bearing known as a hydraulic bearing (or a dynamic pressure bearing) in which oil is used as a lubricant. In the hydraulic bearing, a lubricating oil filling a space between a shaft and a sleeve (a supporter of the shaft) provides a rotation without causing the both to contact with each other. This hardly produces noise in principle with a trace of the rotating shaft being almost round to cause a considerably smaller NRRO compared with that of the bearing with the ball bearings.
FIG. 1 and FIG. 2 are cross sectional views each showing a principal part of a related hydraulic bearing motor. In FIG. 1, there is shown a bearing known as an inverted T type and in FIG. 2, there is shown a bearing known as a T type.
The hydraulic bearing motor 300 shown in FIG. 1 is provided with a hydraulic bearing assembled with the following being taken as prime components, a sleeve (a support) 31 formed with a cylindrical shaft body inserting hole, a frame 32 securing the lower side of the sleeve 31, a cylindrical shaft body 33 having a cross sectional form of an inverted T and being inserted into a space formed by the shaft body inserting holes the sleeve 31 and the frame 32, with a clearance being created between the shaft body 33 and inner walls of the sleeve 31 and the frame 32, a hub 34 securely mounted on an upper portion of the shaft body 33, and oil 35 filling the above clearance. In addition, the hydraulic bearing motor 300 comprises a core 36 laminated with steel plates disposed on the periphery of the sleeve 31, a coil 37 wound onto the core 36, and a magnet 38 mounted on the hub 34 and positioned so as to face the core 36 and the coil 37 the hydraulic bearing motor 300 functions so that a varying magnetic field generated by the core 36 and the coil 37 acts on the magnet 38 to rotate the hub 34 with resulting rotation of the shaft body 33.
In the hydraulic bearing, when the shaft body 33 is in rotation, a pressure is generated in the oil 35. The generated pressure keeps the shaft body 33 away from the sleeve 31 side for rotation. The pressure is generated by dynamic pressure generating grooves formed on the surface of the shaft body 33. The groove is generally known as a herringbone, by which fluid flows therein for being gathered to increase a pressure of the fluid. The fluid with an increased pressure is then made to flow out from the groove to generate a dynamic pressure. The rotated shaft body 33 itself makes the fluid flow in the dynamic pressure generating groove from an entrance side thereof.
The dynamic pressure generating grooves maybe classified into grooves provided on a surface of a radial shaft for gathering the fluid to generate a pressure in the radial direction, and grooves provided on an end face of a thrust shaft for gathering the fluid to generate a pressure in the axial direction of the radial shaft perpendicular to the radial direction. A section of the shaft body inserting hole by which the radial shaft is supported is called as a radial bearing section, and a section of the shaft body inserting hole by which the thrust shaft is supported is called as a thrust bearing section. Here, the thrust bearing section is shown as a region surrounded by the sleeve 31 and the frame 32. Namely, the radial shaft and the thrust shaft are separately provided on the shaft body 33 with dynamic pressure generating grooves for generating dynamic pressures formed on the respective shafts.
On the radial bearing section side, there is provided a function of supporting the shaft body 33 against whirling and a moment thereof being generated. While, on the thrust bearing section side, there is provided a function of supporting a load (disks) stacked on the hub 34 with the centers of the load and the hub 34 on the same axis.
The hydraulic bearing motor 400 shown in FIG. 2 is provided with a hydraulic bearing assembled with the following being taken as prime components, a doughnut-like upper plate 40, a sleeve (a support) 41 formed with a cylindrical shaft body inserting hole having a cross sectional form of inverted T for fitting the upper plate 40, a frame 42 securing the lower side of the sleeve 41, a cylindrical shaft body 43 having a cross sectional form of a cruciform shape and being inserted into a space formed by the upper plate 40, the shaft body inserting hole of the sleeve 41 and the frame 42 with a clearance being created between the shaft body 43 and inner walls of the upper plate 40, the sleeve 41 and the frame 42, a hub 44 securely mounted on an upper portion of the shaft body 43, and oil 45 filling the above clearance. In addition, the hydraulic bearing motor 400 comprises a core 46 laminated with steel plates disposed on the periphery of the sleeve 41, a coil 47 wound onto the core 46, and a magnet 48 mounted on the hub 44 and positioned so as to face the core 46 and the coil 47. The hydraulic bearing motor 400 functions so that a varying magnetic field generated by the core 46 and the coil 47 acts on the magnet 48 to rotate the hub 44 with resulting rotation of the shaft body 43. Also in the hydraulic bearing motor 400, a radial shaft and a thrust shaft are separately provided on the shaft body 43 with dynamic pressure generating grooves for generating dynamic pressures formed on the respective shafts.
In recent years, development is being carried out for mounting the HDD not only on a personal computer but also on a portable information device so that the device is to become multimedia equipment. The portable information device as a target of the development, in order to be provided as being lightweight and compact, requires the HDD to be also provided as being lightweight and compact. In particular, for improving portability, it is also required that the hydraulic bearing motor itself is to be made thin.
In the related hydraulic bearing motors, however, the radial shaft and the thrust shaft were designed and manufactured on condition that they are separately provided. This required a radial shaft to have a certain specified length, so that the radial shaft had a limitation in being made thin. Namely, shortened radial shaft becomes incapable of providing a stiffness for suppressing whirling of the radial shaft. Therefore, in the related hydraulic bearing motor, there was a problem in that it is impossible to satisfy features of exhibiting small NRRO, and vibration and shock resistance while satisfying requirement of making the motor thin.
Accordingly, the present invention was made in view of the foregoing with an object of providing a hydraulic bearing motor that can satisfy features of exhibiting small NRRO, and vibration and shock resistance even when being provided as a thin hydraulic bearing motor.
In order to achieve the above object, the hydraulic bearing motor according to the present invention is characterized by a constitution wherein, in a hydraulic bearing motor comprising:
a shaft body having a radial shaft and a thrust shaft, the radial shaft having a plurality of dynamic pressure generating grooves being formed on an shaft surface for gathering fluid to generate a dynamic pressure in a radial direction of the shaft body, the thrust shaft having a plurality of dynamic pressure generating grooves being formed on an shaft end face for gathering fluid to generate a dynamic pressure in an axial direction of the shaft body, and the shaft body being rotated in a specified direction with the fluid made flow in the dynamic pressure generating grooves; and
a shaft supporting member having a radial bearing section and a thrust bearing section, the radial bearing section supporting the radial shaft with a specified clearance being created between the shaft surface of the radial shaft and an inner wall of the radial bearing section, and the thrust bearing section supporting the thrust shaft with a specified clearance being created between the shaft end face and an inner wall of the thrust bearing section and between the shaft surface of the thrust shaft and an inner wall of the radial shaft supporting section,
the shaft surface of the thrust shaft is also formed with a plurality of dynamic pressure generating grooves for generating a dynamic pressure in a radial direction in the thrust bearing section.
It is preferable that the dynamic pressure generated in the radial direction between the thrust shaft and the inner wall of the thrust bearing section is equal to a pressure which can support whirling of the shaft body and magnitude of an applied load, and the dynamic pressure generated in the radial direction between the radial shaft and the inner wall of the radial bearing section is enough to avoid contact between the radial bearing section and the shaft body.